This invention involves an improvement in the invention disclosed in U.S. Pat. No. 5,081,913 issued Jan. 21, 1992. That invention was directed to an automatic mechanism for opening and closing an air exhaust outlet, according to whether or not air is being exhausted or ventilated therethrough.
Thus, in accordance with the prior invention, when an exhaust fan turns on and creates an over-pressure condition in the air exhaust conduit, the pressure sensing means will be activated. In the preferred embodiment, the pressure sensing means is a vane which swings in response to an over-pressure to close an air bleed outlet, activating a first switch which supplies current to a motor. The motor, will then open the conduit closure or flap. Once the flap is fully open, an interlock means interrupts the flow of current to the motor and holds the conduit closure in a static, "open" mode.
With the flap fully open the over-pressure condition in the conduit may fall in strength and the vane may erroneously indicate that the flap should no longer be in the fully open position. It is for this reason that the prior patent indicates that the this pressure sensing means may be combined with an air flow sensing means so as to keep the said first switch in the static, open mode if air flow is detected simultaneously with only a minimal over-pressure condition.
When the exhaust fan stops, the over-pressure condition in the conduit will drop and the air flow will stop. This causes both the pressure and air flow sensing means to be deactivated. In the preferred embodiment the pressure-sensing means will move, under a spring or gravity bias, to a second position wherein the bleed outlet is open. By this action the electrical interlock holding the conduit closure in its "open" state is over-ridden and a second switching means commences to provide current to the motor in a manner which causes the flap on the conduit to shut.
A second interlock means is provided to interrupt the flow of current to the motor, once the closure means on the conduit is in a fully closed condition. This second interlock may itself be over-ridden and combined with the first switch means to permit current to flow to the motor means, in a closure-opening direction, once the pressure-sensing means is reactivated by a resumption of over-pressure to its first closure-opening position.
The cited prior patent describes a pressure detection mechanism that relies upon a swinging vane that is responsive to an over-pressure condition between the interior of a conduit and the region outside. Reference is also made to an air-flow detecting vane operating in parallel with the pressure detecting vane to control the closing and opening of the closure of the conduit.
This present invention relates to an improvement in the inter-relationship between the two vanes used to control these actions.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with references to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention will then be further described, and defined, in each of the individual claims which conclude this Specification.